Discussion in 'macOS' started by bloodfist, Oct 22, 2005.

  1. bloodfist macrumors member

    Apr 30, 2005
    I just got my new DP 2.3 G5 about almost two weeks ago and I am trying to come up with some sort of backup schedule. Then I thought, hey I can setup a RAID mirror, and not really have to worry about backing up to my externals that often.

    The Disk Utility help has offered the most help so far, Google doesn't bring back much and I didn't find anything on here that had a step by step how to.

    I have also read at various places that setting up a RAID mirror requires a reinstall of OS X to get it to work correctly but disk utility makes no mention of this.

    Can someone who has set up a RAID mirror explain how they did this?


  2. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    A RAID 1 mirror is not a backup, it is a mirror.

    The difference? If you delete a file accidentally, or overwrite a good file with a bad one of the same name, or suffer data corruption from a crash, the damage is done instantaneously to the Mirror drive as well as the main drive. You can't go back even one minute in time to retrieve what it was before the &#%#-up

    What a RAID 1 protects you against is hardware failure of one drive. No more and no less.

    You still need to have an independent, periodic backup to a different disk, ideally one that is not inside the machine.
  3. eva01 macrumors 601


    Feb 22, 2005
    Gah! Plymouth
    i need to get a RAID and a firewire 800 drive

    2 raptor 74Gig drives and a 300GB firewire drive
  4. bloodfist thread starter macrumors member

    Apr 30, 2005
    Well maybe backup was the wrong term to use. I don't really do anything that would require the abilty to recover a file from some obscure date in the past.

    Presently I have 2 external firewire drives that I use for "backup" purposes. Any file that I would like to keep indefinetly I copy to the external drives. If I find that I want the file again, I just plug in the drive and copy it back to my machine. This was when my PowerBook was my main machine and hard drive space was limited.

    Now with this 250GB drive in the PowerMac, space isn't really a concern anymore. There is no need to copy files to an external drive for long term storage. This is where the RAID mirror would come in. With a mirror I essentially have a "backup" of everything on another drive. If one drive fails, my data is intact on the other drive. I am not too sure if I could boot off of one drive alone while the other is in the process of being replaced, I'll have to read some more about it.

    My main question is do I just put another drive in (I can get the exact same model from newegg) and set up the RAID in disk utility or do I have to reinstall OS X to set this up?

    Hopefully this clears up any confusion I may have caused.
  5. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    Again, a RAID mirror is not a backup. Depending on what goes wrong you could lose the data on both drives.

    If you want to be able to recover files, they need to be really copied to another drive or optical media.

    A RAID mirror setup only protects you from a pure hardware failure. It doesn't prevent you from software errors, user errors and the like.
  6. bloodfist thread starter macrumors member

    Apr 30, 2005
    So something in the OS X RAID software could cause both drives to become corrupt and unreadable? Not like the software is prone to such errors but it could happen?
  7. risc macrumors 68030


    Jul 23, 2004
    Melbourne, Australia
    I doubt it, but if something goes wrong with your install RAID 1 isn't going to protect you from that you have to think of RAIDed drives as a single drive, the guys here are just pointing out while RAID 1 is a good idea for hardware redundancy you should still have a backup plan in place to protect your data if something goes wrong during an upgrade, or if a piece of software breaks something, or you delete some thing important. Redundancy and Backup aren't the same thing.
  8. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Well sure: Say you are installing a piece of software, the installer crashes and in the process overwrites a portion of the OS on the drive. In that case, both the drive and its mirror are corrupted.

    I don't know from personal experience, but my assumption (in that the RAID setup (0 or 1) is done in the Disk Utility formatting/partitioning stage) is that the data on the volumes will be lost in the process. Certainly RAID 0 (striping) would wipe out all the existing data. I don't know if you can retroactively attach a RAID 1 mirror to an existing volume without destroying the data - the Apple docs I have been able to find all assume you are starting from empty disks.

    Other tidbits noted en route: Apple does not support an OS booting from a RAID 0 volume. Using the Apple software RAID means that the resulting volumes cannot be partitioned.
  9. RatVega macrumors member

    Oct 14, 2005
    Southern California


    I run in a similar environment but with a RAID, and it's not my first...

    A RAID 1 (mirrored) has only one purpose: it's to keep a "hot" copy of the system and data online in the advent of a hard drive failure in a mission-critical system. Any other use is just a waste of disk space since both copies change in real time whether because you updated or from an error, so you can easily get duplicate bad data instead of the back-up you planned.

    With the current failure rate on hard drives, the likelyhood that you'll actually lose a drive instantaneously is pretty darned low.

    I run a RAID 0 for two reasons: speed and to get a very large monolithic storage area (I do video...). I have an FW "back-up box" that I bring on line periodically to back up critical data. If I was more worried about data loss, I'd be using a utility that did timed back-ups to the external drive.

    BTW, my System and Apps are on a 250GB drive separate from the RAID.

    If you're absolutely committed to doing a mirror, you'll need two additional drives, a SATA controller card, and a mounting scheme (I use a SwiftData RAID rack), so $500-600 should get it done for a 250GB mirror. OS X doesn't support booting from a RAID. It may be possible using SoftRAID, but that's another $150 and a learning curve.

    Or, you could buy a 400GB drive for about half that and back it with your existing FW drives.

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